Adsorption and thermodynamic studies of pure and binary CO2 and N-2 gas components on nitrogen enriched nanostructured carbon adsorbents

摘要

Adsorption isotherms of pure components (CO2 and N-2) on nitrogen enriched nanostructured carbon (UFZ-700) were evaluated at four different adsorption temperatures ranging from 303 to 373 K using a static volumetric analyzer. They were then correlated with the three pure component adsorption isotherm models namely Langmuir, Sips, and dual-site Langmuir (DSL) models. Binary components (CO2-N-2) adsorption equilibria were then predicted by extending Sips and DSL equations empirically along with usage of ideal adsorbed solution theory. Further, it was compared with experimental data obtained from the breakthrough curves by various phase diagrams. Binary system breakthrough data were obtained at four different CO2 feed concentration and four adsorption temperatures (303-373 K) using a fixed-bed column. Sips and DSL adsorption isotherm models fitted well among three pure component adsorption isotherm models indicating energetically heterogeneous adsorbent surface. Because of the difference in adsorptive strengths of CO2 and N-2 molecules, the models extended forms highly under-predicted the amount of CO2 adsorbed over the whole temperature and feed concentration range. Also, ideal adsorbed solution theory failed to describe the mixed-gas adsorption equilibria. With the increase in CO2 gas phase molar fraction, total adsorbed amounts were found to increase, deviation indicating positive from Raoult's law with asymmetric x-y diagrams. Thermodynamic functions such as molar Gibbs free energy change, entropy change, and enthalpy change for the pure component system were numerically evaluated. They indicated the formation of more ordered configuration of CO2 molecules on the adsorbent surface and confirmed the feasibility of adsorption process. (C) 2018 Elsevier Ltd.